The present invention relates to an image transfer apparatus for placing an image sheet and an image-receiving sheet one above the other to transfer an image on the image sheet to the image-receiving sheet.
When a number of sheets are printed by fabricating printing plates formed of plate making material, such as PS plates, from a color original, a color proof is first prepared for so-called color proof operation.
As photosensitive materials for making a color proof, there are known such photosensitive materials as those used in the silver-salt photographic process or electrophotographic process, or using photopolymers. A color proof is produced by exposing an image to such photosensitive materials for printing, then developing the printed image, and finally transferring the developed image to an image-receiving sheet.
At this time, four types of photosensitive materials are employed to prepare image sheets having respective color images of black, cyan, magenta and yellow. Then, these images are successively transferred to the same image-receiving sheet for producing a multi-color image.
Transfer apparatus for successively transferring images on four image sheets to an image-receiving sheet have been proposed in U.S. Pat. No. 4,659,927. With the proposed apparatus, each of the image sheets and the image-receiving sheet are placed on a guide plate with proper alignment, and tentatively secured or tacked together with finger pressure. Then, an operator inserts both the sheets along with a support plate into a nip between a pair of heat rollers of the transfer apparatus. While being held between the pair of heat rollers with pressure, the two sheets are advanced under heating for enabling image transfer.
However, as the place size of image sheets and image-receiving sheets is increased, support plates are also increased in the size and weight correspondingly, thus making it more troublesome to insert support plates into a transfer apparatus along with the image sheets and the image-receiving sheets placed thereon.
Further, a specific working table is required in placing the image sheet and the image-receiving sheet on the support plate, which needs an ampler working space.
A step of aligning the image sheet and the image-receiving sheet on the support plate has been so difficult to carry out that it necessitates a skill of the operator. A difficulty has also been experienced in a step of tentatively securing the sheets with finger pressure, so the step has needed a skill and spent a lot of time as well.
In addition, there has been a fear that when inserting the image sheet and the image-receiving sheet into the nip between the pair of heat rollers of the transfer apparatus along with the support plate, they might be advanced obliquely relative to the direction of insertion. In that event, satisfactory image transfer could not be achieved.